This invention relates to an improved hydroconversion catalyst wherein the improvement is attributed to particular physical characteristics of the alumina-based catalyst, and to hydroconversion processes employing it such as hydrogenation, hydrodemetallization, hydrodesulfurization and hydrodenitrogenation.
It is well known to purify mineral oils such as crude oil, petroleum fractions, shale oils, coal tar distillates, petroleum residues and the like with hydrogen in the presence of a catalyst. Typically the catalyst is deployed in the hydroconversion zone in one or more fixed beds. Often these beds are supported or retained at their inlet or outlet, or both by materials which are inert to the reaction, in order to facilitate even distribution of the feedstock, that is, to prevent or reduce channeling through the catalyst bed; and to trap undesirable materials in the feedstock such as corrosion products and other particulate matter as may be present in the feedstock, in order to prevent such undesirable material from plugging or otherwise deactivating the catalyst bed. The inert materials, which conventionally are in the form of pellets or spheres, typically must be resistant to crushing under the weight of catalyst beds which in an upright reactor may have depths of 50 feet or more.
In many large hydroconversion reactors such as employed in petroleum refining, the inerts will occupy a substantial portion of the reaction zone, e.g. up to 15 to 20% or more of the reaction zone volume. Further, many hydroconversion processes often employ high pressures up to several thousand pounds of pressure requiring expensive pressure reactors. Accordingly, the use of inerts adds to the capital expense of a hydroconversion process both for the reactors which must be oversized to accommodate the inerts and for the costs of the inerts which do not contribute in any significant manner to desired hydroconversion of the feedstock. In addition, it would be highly desirable to increase the efficacy of existing hydroconversion processes by replacing the volume of inerts in the reaction zone with an active catalyst capable not only of performing the functions of the inert materials, but of enhancing the desired conversion process as well. Thus the development of a catalyst which would make it possible to carry out hydrotreatment at greater efficiency and lower cost was desired.